The present invention relates to an alarm terminal device such as a fire alarm terminal device or the like. More particularly, the present invention relates to an alarm terminal device for converting to a digital signal an analog signal indicating a smoke concentration, a gas concentration, a temperature, or other parameter.
It is known to arrange an alarm terminal device such as a fire alarm terminal device such that a detected signal (analog signal) from a temperature sensor or the like is converted to a digital signal which is received by a receiver. Therefore, information other than the detected signal indicating a temperature or the like cannot be obtained. For example, information corresponding to a disconnection or short circuit of a platinum resistor as a major component of a temperature sensor cannot be transmitted through the same transmission line. In order to transmit breakdown data such as data indicating the disconnection or short circuit of the platinum resistor, another transmission line must be provided, or different types of data must be transmitted in accordance with time division multiplexing, resulting in a complex configuration and high cost. Furthermore, according to the conventional alarm terminal device, a sensor output which is less than a predetermined value is transmitted as digital data, e.g., "000", and another sensor output which exceeds the predetermined value is transmitted as digital data, e.g., "111". As a result, a disconnection or short circuit of the platinum resistor cannot be detected upon reception of such data. Since a platinum wire is very thin, the platinum resistor has a tendency to become disconnected or to short-circuit. Therefore, a disconnection or short circuit of the platinum resistor must be constantly monitored.